Contamination prevention in underground storage



June 28, 1960 R. A. KO'BLE 2,942,424

CONTAMINATION PREVENTION IN UNDERGROUND STORAGE Filed March 11, 1957 E N N 3 ELL. q a:

ETHYLENE GAS same TO RESERVOIR 7 HYDROCARBON DETECTOR BLANKET FLOATING S p N g 7 m 'i l I I 1 1 v I h I. V ":1 INVENTOR. R. A. KOBLE BY #Wd 47' TOPNEYS Uni d-St P t CONTAMINATION PREVENTION IN UNDERGROUND STORAGE This invention relates to the prevention of contamina-' tion of materials stored in underground caverns. In another aspect it relates to a method of decreasingthe rate of diffusion of contaminating materials into fluid stored within underground storage caverns'when said contaminating materials are below said stored fluids in the cavern. In still another aspect, this invention relates to' a method of preventing solid hydrate formation in volatile hydrocarbon fluids which are stored underground'o'ver' a-brine displacing medium. Among its rnore specific aspects, thisinvention relates to a method of storing ethylene inan underground storage cavern and displacing it therefrom with brine without danger of contaminatingthe ethylene, and to a'cavern so adapted: v

' Storage of highly volatile or normal-1y gaseous hydro: carbon materialsin vast quantities isa problem in safety 2,942,424 Patented June- 28, 1 960 2 tion of 'm'aterails stored, in underground caverns from liquids lying below such stored materials within the cavern. It is another object of my invention to provide a method of preventing hydrate formation in gaseous or. liquified hydrocarbons stored underground over a brine displacement medium. Still other objects are to provide a means and a method of storing ethylene in an underground storage cavern and displacing said ethylene with brine while maintaining the moisture content of the ethylene at a minimum. Other objects, advantages and features of my invention will be apparent to those .skilled in the art from the following description and the drawing which depicts schematically one embodiment of my invention.

While'my invention can be applied broadly to prevent contamination within underground storage caverns of materials stored therein, when the cavern contains contaminating fluids lying below the stored material, it is of particular importance in-preventing the contamination of ethylene stored in such an underground cavern by-moisture and/ or oxygen from the brine solution which and economicsfor which underground caverns in intpervious formations" provide a convenient, solution.

Underground caverns [have likewise been found to pro. vide. satisfactory storage for othervola tile materials, such asfammonia, which should be stored under pressure. ,In petroleum product storage applications, it is convenient to use brine as a displacing. medium, especially where thecavern has been formed by dissolutio n of a salt formation withwater, and the brine is, therefore, readily available. Even in applicationswherebrine is not .used. as" the displacing medium but water has been used to form the cavern, such as for ammonia storage, it isvirtnally impossible to completely remove all' brine from the floor of the cavern.. Hence, in these. andother situations there becomes a serious contamination probe lenrof the storedproduct from the foreign material lo cated in the .lower portion ofthe cavern. Of particular difficulty in the storage "of ethylene and LPG is the formation of a solid hydrocarbon hydrate which blocks the pipes asthe hydrocarbon is'jrernoved fromthe storage ca w 7; i

According toiny invention, these and other problems, of contamination of stored materials within ,an underground storage cavern' can-be greatly reduced when thejcontaniinating material isj heavier thanthe stored materialjand'thuslies belo'w' the storedmaterial within the. 'caven'i., ,Thisj endfis accomplished by. providing a,

. fluentlmass havinga density less than the contaminating material but-greater than'thfejstored fluid, which fluent mass forms ,a barrier atthe interface of the contaminatinghnater'ial.and stored fluid thus preventing or sub stantially decreasingtl'ie 'r'atefof diifusion of contaminant into; the stored fluid. Aninter faeial barrier ,thus' formed blankets the surface. of the lowericontaniinating liquid and readily' assumes the configuration of the cavern to provide; asatisfactory seal. This fluent mass canbe a finely dividedor particulate solid, a relatively nonvolatile liquid or some intermediate form such as a solid-liquid mixture, a semi-solid, or a matted, stringy or gelatinous mass... 1':

It is an object of my invention to prevent contaminais commonly used to displace the ethylene from the cavern. When ethylene is to be used as a monomer for catalytic polymerization it must be maintained relatively free of oxygen and moisture which are catalyst poisons. Likewise, ethylene within the cavern must be kept. free of moisture to prevent the formation of a solid hydrate upon removal of the ethylene from the cavern. In such a storage application the temperature of the ethylene within the cavern is maintained above the temperature of hydrate formation. An' application of this i 7 type is shown schematically inthe attached drawing.

Referring now to this drawing, an underground storage "cavern'in an impervious salt formation isindicated by thenumeral 10. Within storage cavern 10 ethylene 'gas 11 is stored over brine 12 Whichis used as a displacing trnedium in the operation .of the cavern which will subsequently be described. According to my invention contamination of the ethylene gas by moisture from the brine. is prevented by providing a protective floating blanket 13. Materials comprising this blanket will be described in greater detail later. Various particulate solids and. liquids which will form a fluent mass that covers the surface of the brine and readily assumes the configuration of the cavern are suitable. Relatively thin layers of such materials on the brine surfaceare quite effective in reducing the moisture diffusion rate from v the brine to the ethylene gas.

In the operation of the underground storage cavern ing positioned therein concentrically positioned lengths of. tubing 16. and 1'7. Casing 14 extends from the surface' of the earth to] the tbpofZ-thestorage cavern and is cemented 'to the. surrounding formation. This casing provides the ndeafis .for the ethylene gas to enter and leave the. underground cavern. Tubings 16 and 17 extend into the lower; portion "of 'thelcavern and are .used to remove or introduce brineto the cavern thus displacing the ethylene gas. While both tubings 16 and 17 are used in the formation of the cavern, only one, preferably tubing 17, is needed in itsoperationa .4

'Ethy leneis pumped from the'refinery via line 18and through valve 19'into line 20 passing through valve 21,.

through tubing 17., Brine rises through tubing 17, enters check valve 22 and valve 25; Ethylene thus enters the annular space between casing 14 and outer tubing 16 and is forced into storage cavern 10.. As ethylene enters the storage cavern, brine isdisplaced from the cavern line 23 andpasses through safety valve 24, and valve 26,

continuing on through line '27 to the brine reser'voir 28.

brine is pumped from reservoir 28 through line 29 by pump 30 and passed through line 31 to heat exchanger 32, wherein the brine can be heated in order to keep the ethylene gas in casing 14 above the temperature at which solid hydrate formation occurs. One method of reducing the possibility of solid hydrate formation in the ethylene is to maintain the temperature of the gas, by indirect heat exchange with the brine, above that temperature at which the solid hydrate tends to form. This precautionary step'is further aided by the protective layer of my invention which forms a barrier at the interface between the ethylene and the brine, thus reducing the rate at which the ethylene gas picks up moisture from the brine.

Heated brine passes from heat exchanger 32 through lines 33 and 34 and safety valve 36 into the outer tubing 16. The brine thus passes through the annular space between tubing 16 and 17 and enters the storage cavern displacing therefrom the ethylene gas. As the heated brine passes downwardly to the cavern it is in heat exchange relation through the walls of tubing 16 with the ethylene gas as it rises from the cavern. In this manner the ethylene can be kept at a temperature above the solid hydrate formation temperature, provided the moisture content of the ethylene is not too great. Brine can also be passed from line 33 through valve 37 and into line 23 from which it passes into inner tubing 17 thence downwardly into the storage .cavern. Ethylene is thus displaced through casing 14 into line 20. Check valve 22 forces the gas to pass through line 39 and valve 40 into filter and separator 41, which serves as a safety device to remove moisture from the ethylene before the gas passes on to its point of usage and final purification steps- The use of filter and separator 41 is optional when practici ing my invention and can be lay-passed. Ethylene from the filterand separator passes through line 4-2, check valve 43 and valve 44 into line 2% again, and passing through valve the event the brine level is forced below the bottom openings of tubings i6 and 17, is prevented by hydrocarbon detector 35, positioned todetect hydrocarbon in line 2-3 and in response thereto to close valves 24 and 36. Detector. 38 can bea dielectric instrument, such as an Enniscope which is an interface indicator manufacturecl by Oil Well Water Locating Company of Long Beach, California. 7 I

While my invention can be applied to many underground storage situations, the above desc ribed embodiment is set forth as one of many possible applications and my invention should not be interpreted as limited to this specific case. The operating. conditions of temperature and'pressur'elof the above described embodiment can vary widely, and the value of my invention is not dependent upon any specific set, of. underground storage conditions. .Howevenby way of further exemplification,

the following operating conditions are set forth in connec tion with the embodiment described by the drawing.

Suitable operating conditions for the ethylene within. the cavern are a temperature of v 130 to 135? F. and a pressure of about l400 to 1700 pounds per square inch absolute. Ethylene as it is introduced to the cavern will generally be about 50 to 80 F. Brinein the reservoir has'atemperature of about 5091. and is heated toabout 70 to 90; F. in the heat exchangeri, Ethylene as it is introduced into the 'cavern is heated by indirect light mineral and resinous materials.

after withdrawal. Pipe line pressures vary from about 1600 pounds per square inch absolute at the cavern outlet to about 300 pounds per square inch absolute in the pipe line to the point of usage. Hydrate formation generally occurs at temperatures of about 50 to 70 F. assuming, of course, that the .gas is saturated at these temperatures. For example, at a temperature of 70 F. and a pressure of 1200 pounds per square inch absolute, ethylene gas is saturated when the moisture content thereof reaches 60 parts per million. This is a possible pipeline condition and is, of course, what the practice of my invention seeks to avoid by forming a vapor barrier at the ethylene-brine interface.

The barrier forming material can be any inert, nondeleterious solid, semisolid, immiscible liquid or mixture thereof which has a density less than the lower contaminating material and a density above that of the material to be stored in the cavern. I prefer to use for this purpose ,finely divided or particulate solids which float upon brine forming a layer thereon which readily conforms to the shape of the cavern. Suitable materials are solid polymeric or plastic chips or pellets, for example, polyethylene or polystyrene flakes, granules, or pellets. Tiny hollow spheres of this plastic as produced by spray cooling are also suitable. Particulate solids such as silica, alumina, zirconia or thoria can also be used. These granular materials commonly used as catalyst carriers alone or in combination are especially suitable when sealed with a deposit of polymer to lower their apparent density and prevent soaking from the brine. Thus a source of material is spent catalyst from a polyolefin polymerization process employing catalysts of this type. Popped volcanic ash is suitable as well as various other These particulate solids can range from fine powders of less than one thousandth of an inch in diameter to granules as large as of an inch in diameter. The shape of the particles can vary widely, for example from spherical to irregular crystalline shaped particles, but fiat-surfaced particles ness of the protective layer will vary widely, depending largely upon the cross sectional area of the cavern at the brine level. 7

Also suitable art inertand non-volatile liquids which will form a layer upon the brine beneath the storage materiall Examples of such materials are cetyl alcohols, mineral and vegetable oils, polyethylene glycol, polypropylene glycol, and other liquid polymers as well as various waxes and the like. Liquid polyethylene is an ideal fluid to provide the protection needed. The criteria in selecting aprotective liquid layer is low density (less than 1.18 poundst per cubic foot when used over brine), low vapor pressure, and insolubility or immiscibility with Water.

The protective material can be introduced with the brine or with the stored fluid. In certain applications, as in the preparation of an underground cavern for ammonia storage, the protective layer should be introduced after the cavern has been formed to its proper size and before all of the brine has been removed therefrom. In this way, the protective mass forms its layer over the brine surface and should any brine be captured in pockets or recesses within the cavern so as to prevent complete removal thereof, its surface will be covered with this protective, relatively impervious layer which helps prevent contamination of the ammonia when it is subsequently stored within the cavern.

Other applications of my invention will readily become apparent to those skilled in the art for the prevention of contamination of materials stored in underground caverns without departing from the scope of my invention. To further describe my invention, the following examples and data are presented for exemplary purposes only and these should not be interpreted as limiting my invention unduly. V v v r 1 EXAMPLES Ethylene is stored in an underground cavern in a manner similar to that described in connection with the attached drawing. vThe cavern is formed in a subterranean impervious salt formation at a depth of 2500 feet, the average diameter of the cavern is 59 feet and its total depth is 410 feet. Brine having'a concentration of 27 weight percent sodium chloride, fills the lower portion of the cavern to a point 200 feet from the top of the cavern. The remainder of the cavern, that is, the top 200 feet of the cavern, is filled with ethylene gas at a pressure of 100 atmospheres and a temperature of 130 F.

In determining diffusion rates for moisture from the brine to the ethylene gas, two conditions are considered. First, under the perfectly quiet condition (that is, when there is neither introduction nor removal of material from the storage cavern) there is no temperature, gradient and only an extremely slight moisture gradientwifhin the stored ethylene so that the movement of vapor is only by molecular difiusion. Second, the disturbed condition-is considered, for example, when ethylene at 70 F. is being introduced to the cavern. In such an instance a 50 percent density diiferential exists in the ethylene in .the cavern, thereby producing eddy currents and greatly increasing the possibility of moisture diffusion, as shown in Table I.

To protect the ethylene gas from moisture contamination suflicient liquid polyethylene is introduced to the cavern to form a layer of about 4.5 inches in thickness on the surface of the brine over the 59 foot diameter. The liquid polyethylene, having a lower density than the brine, forms a protective barrier at the interface between the brine and the ethylene. gas and is sufliciently fluid to readily assume the configuration. of the cavern thus providing acomplete seal. The moisture difiusion rates with this blanket are compared with the unprotectedcondition in Table I.

Table l Difiusion Rates of Conditions Within Cavern Moisture From Brine to Ethylene Parts per Conditions of Brine Million Surface and Ethyl- Initial Moisture Con- Pounds (Moisture ene Gas tent of Ethylene per Hour in Ethylone per Hour) 1. N0 Blanket Quiet- 60 p.p.m. 100 feet. 0.0008 to 0.000097 to above Brine. 0.002 0.00024 2. Blanket Quiet -.do 0.0001 to 0.000012 to 0.0007 0.000085 8. No Blanket Quiet. 30 p.p.m. Bulk Con- 0.007 to 0.00085 to tent. 0.01 0.0096 4. No Blanket Dis- .do 2.0 to 0.24 to ur e 10.0 0.96 6. Blanket Disturbed. 30 p.p.m. at Blanket-. 0.00016 to 0.000019 to As shown by the data of Table I, the diifusion rate of moisture, from the brine to the ethylene under quiet conditions isseveral times greater for the unprotected brine surface than for the brine blanketed with a polyethylene layer (1 and 2). A more striking contrast is noted for to remove about 0.001 poundof water perhour, which is a blanketed diffusion rate when ethylene contains 30 parts per. million of moisture, it is necessary to remove an average of only about 40 pounds of ethylene per hour. This is ordinarily less than normal operational breathing. For a comparable condition'without the protective blanket, it would be necessary to remove moisture from the cavern at a rate of about 6 pounds per hour. To accomplish this by breathing ethylene would require processing 200,000 pounds of ethylene per hour, which would be very impracticable. Thus, it is evident that the protection afforded by the practice of my invention is quite efiective and solves a serious contamination problem in the storage of materials in underground storage caverns.

I claim:

1. A method of reducing hydrate formation on removal of hydrocarbon gases from underground storage over brine which comprises covering the surface of said brine with a layer of finely divided polymeric solids having a density less than said brine but greater than said hydrocarbon gases, thereby forming a moisture barrier at the interface of said brine and said hydrocarbon gas.

, 2. A method of reducing the degree of contamination of a fluid product stored in an underground storage cavern wherein said underground cavern contains in the region below said stored product a contaminating aqueous liquid which tends to contaminate the stored product by difiusion of vapors thereinto which comprises introducing into said storage cavern, in a sufficient quantity to cover the surface of said contaminating liquid, inert, non-deleterious,

particulate solid material having a particle size of less than about A; of an inch in diameter, said particulate material being at least superficially polyolefinic, thereby forming on the surface of said contaminating liquid a non-'wettable barrier to vapor diffusion.

3. A method of maintaining the moisture content of ethylene as low as possible when said ethylene is stored V in an underground storage cavern over brine used as a the-disburbed condition. In this case very little change occurs for the blanketed surface (2 and 5); whereas, for the unprotected interface the diffusion rate under the disturbed conditions is in the order of 1000 times greater than for the quiet conditions (3 and 4).

It is evident that the quantity of moisture diffusing through the polyethylene blanket is small enough that a condition of low moisture content can be maintained by periodically breathing some of the ethylene from the cavern and replacing it with dry ethylene. For example,

displacing medium within said cavern, which comprises introducing into said cavern a sufiicient amount of finely divided solid polyethylene to form a layer on the surface of said brine, said layer being in the range of about 1 to 5 inches in thickness and being conformable to the configuration of the cavern, thereby forming an efiective barrier to moisture transmission at the interface between the brine and the ethylene within the cavern.

4. A method according to claim 3 in which said polyethylene has a particle size and range of about 0.001 to 0.125. inch in diameter.

' 5. An underground storage system comprising an underground storage cavern in a salt formation, brine, as a displacing medium occupying the lower portion of said cavern, means for increasing and decreasing the quantity of said brine in said cavern, a layer of. inert, solid particles having solid hydrocarbon polymer on at least their surfaces blanketing the surface of said brine forming a non-wettable vapor barrier thereon, hydrocarbon stored placement liquid in the lower portion of said cavern,

said liquid having a greater density than said product, introducing an inert, fluent mass of resinous particulate solids into said cavern in sulficient amount to form a protective'blanket over the surface 'of said liquid at the maximum cavern cross-section, said mass havinga density intermediate that of said liquid and said product, and supplying additional amounts of said liquid into said cavern thereby raising the lev el.0f said blanket in said cavern and'displacing product from the cavern without contacting the product was said liquid. 8. A method according to claim 7 wherein said fluent mass is particulate polyethylene solids.

9. A method according to claim 7 wherein said fluent mass is particulate resin-coated mineral solids.

10. A method according to claim 7 wherein said product is ethylene and said liquid is brine.

References Cited in the file of this patent UNITED STATES PATENTS Tracy T? ..'May 29, 1934 Krewer Feb. 20, 1951 FOREIGN PATENTS Norway June 30, 1941 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION June 28, 1960 Patent No., 2q942 424 Robert Ao Koble It is herebj certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7. line 3, for "was" read with Signed and sealed this 4th day of April 1961B 3%? ERNEST W. SWIDER ARTHUR W. CROCKER Acting Commissioner of Patents L, It Attesti 

